1. Field of the Invention
This invention relates to secondary image forming type finder optical devices and, more particularly, to secondary image forming type finder optical devices provided with an objective lens solely used therefor separately from the photographic lens and having a predetermined optical total length, which devices are suited to, for example, electronic still cameras or video cameras.
2. Description of the Related Art
Recently, a variety of kinds of photographic systems on the electronic still camera which magnetically records video information in the small-sized floppy disc have been proposed. Of these proposals, particularly for the finder optical device, various types are adopted.
The electronic still camera differs largely from the conventional camera for silver halide photosensitive material in the shape of the entirety of the camera depending on how to arrange the floppy disc in the camera body.
For example, in the case of containing the floppy disc in a chamber whose plane is parallel to the optical axis of the photographic lens, the shape becomes an axially elongated one as in the motion video camera of the unified type of recorder and reproducer, or the like.
The so-called reverse Galilean finder optical device which has so far been suited well to the external finder optical device for the silver halide camera, and the real image finder optical device of the primary image forming type using the prism for non-reverse erecting image, when applied to the electronic still camera, etc., because of their optical total length being too short, have given rise to, for example, the following problems.
That is, to secure a sufficiently long eye point by arranging the eyepiece lens of the finder optical device at or near the rear plane of the camera, the shortage of the optical total length of the finder optical device causes the front vertex of the objective lens to be arranged in a considerably secluded position from the front plane of the camera. For this reason, to secure the finder light beam without eclipse, the size of the opening portion for the finder optical device in the front panel of the camera housing must be increased, which calls for an increase of the distance from the optical axis of the photographic lens to that of the finder optical device. Thus, a problem of intensifying the finder parallax and others arose.
The conventional secondary image forming type finder optical devices for use in the video cameras or the like, on the other hand, generally become too long in the axial direction. Hence, they are not very suited to be used in, for example, electronic still cameras.